The effects from thermal treatment

The effects from thermal treatment on the angiogenic activity of natural rubber are illustrated in Figures 3.a)-f),
which show the membranes placed in the CAM for heating
temperatures ranging from 55-105 ◦C. A qualitative examination of the CAM images shows no change in the vessels
density for temperatures between 55o and 65 oC. In contrast,
for temperatures between 75◦ and 85 oC, a red region marked
by an arrow appears in Figures 3 e)-g), which is indicative
of rubber angiogenesis. The difference is clear upon comparing Figures 3d and 3e with the control membranes. For
membranes heated from 95o-105oC no changes in the vessel
density could be observed in the CAM companying with the
control membranes.
The angiogenic activity may be evaluated quantitatively
by counting the number of vessels in the graph of Figure 4.
The amount of vessels presented shows an average of the fifteen experiments performed for each temperature. The error
bars on Figure 4 show the standard deviation (SD) of data. In
spite of the dispersion in the data points (to be discussed below), the activity for the thermally-treated NR membranes in
Figure 3 is always higher than the control sample made with
synthetic material (black dashed line). An optimized temperature for treating the membranes is between 65oC and 85oC,
where angiogenesis activity was maximum.
The large dispersion in the data (i.e. large error bars) may
have several sources. First, NR does possess different properties depending on the period of collection (seasonal variation) and storage time [24,26,31]. Indeed, an inspection of
our results points to differences in the activity for membranes
stored for different periods of time. This may be due to the
poor stability of non-rubber constituents of NR, especially
in the presence of ammonium [31]. Most affected are the
lipids, which are major components surrounding the rubber
particles in the latex. The latex used here was collected in
three different seasons over 15 months of studies. Though
we took precautions in keeping the samples in a refrigerator and with ammonium to minimize errors, variations could
still exist. In addition, non-homogeneity in the membranes
was observed even for samples prepared with the same latex,
in the same day